Overproduction of a 21 Kda membrane protein (p21) has been observe in several mammalian tumors and is correlated with ras gene amplification. In the experimental system under study, the Y1 mouse adrenal carcinoma, there are approximately 30 copies of an apparently normal Ki-ras gene and a correspondingly high level of p21. The main goals of this study are to develop systems to specifically inhibit p21 synthesis and to test whether such inhibition can produce a reversal of the transformed phenotype. Specific goals are as follows: (1) Optimize the transcription of full- length antisense Ki-ras sequences (from the plasmid pIFN-ras described in the preliminary experiments) in Y1 cells and confirm that these hybridize in a specific manner with Y1 Ki-ras mRNA and inhibit p21 translation. (2) Construct additional anti-ras plasmids which transcribe partial antisense Ki-ras sequences specific for certain areas of the mRNA and test their effectiveness on p21 inhibition both in vitro and in cultured cells. (3) Construct sequence specific anti-ras oligonucleotides to various regions of Ki-ras mRNA and test their effectiveness on p21 inhibition both in vitro and in cultured cells. (4) Examine the consequences of p21 reduction through assessment of properties of Y1 cells associated with their transformation. Among these would be changes in growth rate, growth factor requirements, karyotype (e.g., loss of DMs or HSR) degree of malignancy and ability to induce tumors in nude mice. (5) Determine the effectiveness of 7antisense hybridons (Ki-ras plasmid constructs or oligonucleotides) on the translation of p21 in other cell lines including those with overexpressed Ki-ras mRNA but an unamplified Ki-ras gene and those with a mutated ras gene.